The transparent wings of tiny parasitic wasps and small flies are remarkably thin, only a few hundreds nanometers thick, and may appear to have a simple structural airfoil design. The thesis deals with new findings about structural color reflections and the ultrastructure of such tiny transparent wings of parasitic wasps. The main discovery is that when seemingly transparent insect wings are viewed against a dark background they display vivid and stable structural color patterns due to optical interference. The patterns are coined with a new term as Wing Interference Patterns (WIPs). It is suggested that small wasps may have evolved specific color patterns that are utilized for visual signaling, for instance by displaying their wings to each other during courtship much in the same way as larger insects with colorful wings (e.g. butterflies) do. Such WIPs lack pure red but may contain ultraviolet light and fit very well to the color vision of most small insects. The visible (to humans) colors displayed are characteristic and identical to the colors one can see on the surface of a soap bubble. But unlike the constantly changing color reflections from soap bubbles WIPs displayed on insect wings are optically stabilized by the thickness profile and specific microstructures of the wing membrane. These factors ensure that the wings display the same color and pattern under different angles of view. Since the WIPs are very diverse among small wasps and often seem to be specific for a species they provide new characters useful for species identification and classification of insects, especially among closely related and otherwise very similar species that live together in nature. In several such cases tiny parasitic wasps appear to have evolved distinct patterns only in the male wings, while the females are similar between species. This suggests that the females chose mating partner based on their WIPs and that these color patterns are an important but previously largely overlooked part of insect biology and evolution.